U.S. patent application number 14/243299 was filed with the patent office on 2014-07-31 for coordinating power distribution line communications.
This patent application is currently assigned to Landis+Gyr Technologies, LLC. The applicant listed for this patent is Landis+Gyr Technologies, LLC. Invention is credited to Damian Bonicatto, Rolf Flen, Chad Wolter.
Application Number | 20140211867 14/243299 |
Document ID | / |
Family ID | 48654538 |
Filed Date | 2014-07-31 |
United States Patent
Application |
20140211867 |
Kind Code |
A1 |
Wolter; Chad ; et
al. |
July 31, 2014 |
COORDINATING POWER DISTRIBUTION LINE COMMUNICATIONS
Abstract
Aspects of the present disclosure are also directed towards a
method that includes maintaining a transmission period which has a
start time and an end time synchronized to metrological time.
Further, this method, in response to the start time, begins
transmission of a frame, which includes a plurality of symbols.
This transmission occurs over power distribution lines that carry
power using alternating current (AC). This method also includes
synchronizing a transmission time for each symbol of the plurality
of symbols according to a time-based parameter of the AC. In
response to reaching an end of the frame, a synchronization symbol
period is determined for a synchronization symbol, as a function of
the transmission times, for the plurality of symbols and time from
the end of the frame to the end time. The synchronization symbol is
then transmitted on the power distribution lines.
Inventors: |
Wolter; Chad; (Breezy Point,
MN) ; Flen; Rolf; (Pequot Lakes, MN) ;
Bonicatto; Damian; (Pequot Lakes, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Landis+Gyr Technologies, LLC |
Pequot Lakes |
MN |
US |
|
|
Assignee: |
Landis+Gyr Technologies,
LLC
Pequot Lakes
MN
|
Family ID: |
48654538 |
Appl. No.: |
14/243299 |
Filed: |
April 2, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13334502 |
Dec 22, 2011 |
8693605 |
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14243299 |
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Current U.S.
Class: |
375/257 |
Current CPC
Class: |
H04B 3/542 20130101;
H04L 7/0091 20130101; H04J 3/0638 20130101; H04B 2203/5408
20130101; H04B 2203/5441 20130101 |
Class at
Publication: |
375/257 |
International
Class: |
H04B 3/54 20060101
H04B003/54; H04L 7/00 20060101 H04L007/00 |
Claims
1. A method useful for coordinating communications between multiple
endpoint devices and multiple collector devices, the communications
occurring over power distribution lines that carry power using
alternating current (AC), the method comprising: communicating data
from the collector devices to the endpoint devices over the power
distribution lines using a communication protocol that uses a first
timing and a second timing, the first timing being a parameter that
indicates when data frames are to be transmitted and the second
timing being a parameter that indicates when symbols within the
data frames are to be transmitted; at each collector device,
maintaining a collector network time using a locally generated time
base; determining the first timing and the second timing based on a
frequency of the AC; and providing the collector network time to
the endpoints devices.
2. The method of claim 1, further including the steps of
calculating the time from the end of a first frame, as determined
by the second timing, to the start of a second frame, as determined
by the first timing; and determining how many synchronization
symbols can be transmitted before the start of the second frame,
the number of synchronization symbols being determined based upon a
rate of symbol transmission for the first frame and the calculated
time.
3. The method of claim 1, wherein the collector network time is
adjusted in response to a standardized time that is maintained
external to the collector device.
4. The method of claim 1, wherein the first timing defines when
data frames are transmitted, and thereafter, data symbols are
transmitted in response to a detected frequency of the AC.
5. The method of claim 1, wherein the data symbols are encoded
using one of amplitude shift keying, quadrature phase shift keying,
differential phase shift keying and frequency shift keying.
6. The method of claim 5, further including a step of sensing the
frequency of the AC carried on the power distribution lines by
periodically operating a software code module to sense a signal
value of the AC, wherein the software code module is periodically
operated at a rate that is sufficiently fast to provide
synchronicity for the encoded symbols to be decoded at an endpoint
device using other software code module to sense a signal value of
the AC.
7. The method of claim 6, wherein the rate is over 1 KHz.
8. The method of claim 1, wherein the step of the communicating
data from the collector devices includes communications to at least
a thousand endpoints from one of the collector devices.
9. The method of claim 1, further including a step of determining a
frequency of the AC by one of sensing a zero-crossing event and
sensing a minimum/maximum signal event.
Description
BACKGROUND
[0001] Service providers utilize distributed networks to provide
services to customers over large geographic areas. For example,
power companies use power distribution lines to carry power from
one or more generating stations (power plants) to residential and
commercial customer sites alike. The generating stations use
alternating current (AC) to transmit power over long distances via
the power distribution lines. Long-distance transmission can be
accomplished using a relatively high voltage. Substations located
near the customer sites provide a step-down from the high voltage
to a lower voltage (e.g., using transformers). Power distribution
lines carry this lower-voltage AC from the substations to the
endpoint devices customer sites.
[0002] Communications providers may utilize a distributed
communications network to provide communications services to
customers. Similarly, power companies utilize a network of power
lines, meters, and other network elements to provide power to
customers throughout a geographic region and to receive data from
the customer locations (e.g., including but not limited to data
representing metered utility usage). A system can provide these
reporting functions using a set of data-collecting devices
(collectors) that are designed to communicate with nearby endpoint
devices. However, data communication between a command center,
collectors and many thousands of endpoint devices over power
distribution lines can be a particularly challenging issue. The
sheer number of endpoint devices contributes to a host of issues
including synchronization, communication bandwidth and cost
concerns. Other problems relate to signal interference and
coordination between communicating devices.
SUMMARY
[0003] The present disclosure is directed to systems and methods
for use with coordinated communications between devices and over
power distribution lines. These and other aspects of the present
disclosure are exemplified in a number of illustrated
implementations and applications, some of which are shown in the
figures and characterized in the claims section that follows.
[0004] Coordinating data communications between a data-distributing
device, such as a collector, and many endpoint devices over power
distribution lines can be a particularly challenging issue. For
certain applications, the sheer number of endpoint devices can
contribute to a host of issues including synchronization,
communication bandwidth and cost concerns. These and other issues
can be appreciated in connection with one or more of the
embodiments discussed herein.
[0005] Example embodiments of the instant disclosure include
various methods and apparatuses. Consistent with the instant
disclosure, certain embodiments are directed towards a method
useful for coordinating communications between multiple endpoint
devices and multiple collector devices. The communications between
these endpoint devices and collector devices occurs over power
distribution lines (carrying power using alternating current (AC)).
In this method for coordinating communications, data is
communicated over the power distribution lines, from the
data-collecting (or collector) devices to the endpoint devices,
utilizing a protocol that is defined by a first timing and a second
timing. The first and second timing can be used to indicate when
data frames are to be transmitted and when the symbols within the
data frames are to be transmitted. Further, the method includes
generating a collector clock at the collector (e.g., using a local
oscillator circuit), and, using the collector clock as a time base,
maintaining a collector network time. In certain embodiments, the
first timing is determined from the collector network time (at each
collector device). Additionally, at each collector device, the
frequency for the AC carried on the power distribution lines can be
tracked. The second timing is determined from the tracked
frequency. Moreover, the method, of the instant embodiment,
includes adjusting an endpoint network time, at each endpoint
device, in response to time-indicating packets/data received from a
collector device.
[0006] In certain embodiments, this method can be useful for
coordinating communications that can include additional steps. For
example, the method can further include calculating the time from
the end of a first frame (as determined by the second timing) to
the start of a second frame (as determined by the first timing). An
additional step of determining how many synchronization symbols can
be transmitted before the start of the second frame is also
included with the step of calculating the time from the end of the
first frame to the start of the second frame. The number of
synchronization symbols is determined based upon the rate of symbol
transmission for the first frame and the calculated time. The
network times, utilized in this method, can be periodically
adjusted in response to an externally-maintained standardized
time.
[0007] In other example embodiments, the first timing defines when
data frames are transmitted, and thereafter, data symbols are
transmitted in response to the AC (e.g., a symbol periodicity is
adjusted based upon a frequency of the AC). The data symbols used
in this method can be encoded using, as a non-limiting example,
quadrature phase shift keying (QPSK). For embodiments using QPSK or
other encoding protocols, the AC can be used as a time base by
periodically/repeatedly executing a software code module, such as
an interrupt service routine (ISR), that monitors a signal value of
the AC. This code/ISR can be repeatedly called at a rate that is
sufficiently fast to provide synchronicity for the encoded QPSK
symbols, the synchronicity being relative an endpoint device that
uses another interrupt routine to generate a AC-frequency time base
that is used to decode the symbols.
[0008] Embodiments of the present disclosure are also directed
towards a method that includes maintaining a transmission period
which has a start time and an end time synchronized to network
time. Further, this method, in response to the start time, begins
transmission of a frame, which includes a plurality of symbols.
This transmission occurs over power distribution lines that carry
power using alternating current (AC). This method also includes
synchronizing a transmission time for each symbol of the plurality
of symbols with a corresponding signal transition of the AC. In
response to reaching an end of the frame, a synchronization symbol
period is determined for an adjusted synchronization symbol, as a
function of the transmission times, for the plurality of symbols
and time from the end of the frame to the end time. The adjusted
synchronization symbol is then transmitted on the power
distribution lines.
[0009] In certain specific embodiments of this method, each symbol
of the plurality of symbols has a common symbol period. Further,
the symbol period of the synchronization symbol is less than the
common symbol period. The symbol, of the plurality of symbols, in
certain example embodiments of this method are further defined as
having a common symbol period. In those instances, a
synchronization symbol period is determined based upon a number of
symbols of the common symbol period that can be transmitted in the
time from the end of the frame to the end time.
[0010] Embodiments of the instant disclosure are also directed
towards a device that includes a network time clock circuit, a
system time clock circuit, and a processing circuit. The network
clock circuit, of this device, is responsive to a network
time-of-day, and the system time clock circuit is responsive to a
frequency of an alternating current that is carried on power
distribution lines. The processing circuit is designed to determine
a transmission period having start and end times determined by
using the network time clock. Further, the processing circuit is
configured to begin transmission of a frame including a plurality
of symbols, in response to the start time and over power
distribution lines that carry power using alternating current (AC).
The processing circuit is designed to synchronize a transmission
time for each symbol of the plurality of symbols to the system time
clock. In response to reaching an end of the frame, the processing
circuit is designed to determine a symbol length for a
synchronization symbol as a function of time from the end of the
frame to the end time and transmission times for the plurality of
symbols. The processing circuit is configured to then transmit the
synchronization symbol over the power distribution lines.
[0011] The above summary is not intended to describe each
illustrated embodiment or every implementation of the present
disclosure. The figures and detailed description that follow,
including that described in the appended claims, more particularly
describe some of these embodiments.
BRIEF DESCRIPTION OF FIGURES
[0012] Various example embodiments may be more completely
understood in consideration of the following detailed description
in connection with the accompanying drawings, in which:
[0013] FIG. 1 is a block diagram of an example network environment
in which endpoints communicate data with collector units,
consistent with embodiments of the present disclosure;
[0014] FIG. 2 depicts a block diagram for a device for coordinating
communications on power distribution lines, consistent with
embodiments of the present disclosure;
[0015] FIG. 3 depicts a timing diagram for frames transmitted over
power distribution lines, consistent with embodiments of the
present disclosure;
[0016] FIG. 4 depicts a timing diagram for coordinated
transmissions, consistent with embodiments of the present
disclosure;
[0017] FIG. 5 depicts a flow diagram for an ISR, consistent with
embodiments of the present disclosure; and
[0018] FIG. 6 depicts a flow diagram for an AC line-frequency ISR
that can be used to determine the average line frequency of that
AC, consistent with embodiments of the present disclosure.
[0019] While the disclosure is amenable to various modifications
and alternative forms, examples thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
disclosure to the particular embodiments shown and/or described. On
the contrary, the intention is to cover all modifications,
equivalents, and alternatives falling within the spirit and scope
of the disclosure.
DETAILED DESCRIPTION
[0020] Aspects of the present disclosure are believed to be
applicable to a variety of different types of devices, systems and
arrangements for coordinating communications between multiple
levels of devices using power distribution lines as communication
carriers. While the present disclosure is not necessarily limited
to such applications, various aspects of the disclosure may be
appreciated through a discussion of various examples using this
context.
[0021] A particular use of power line communications relates to
utility meter reading applications. In utility meter reading
applications (as well as other applications), there can be millions
of endpoint devices providing coordinated readings. Communicating
downstream to so many endpoints represents a daunting task, which
is worsened by the communication constraints caused by the use of
power distribution lines. For instance, there can be constraints
relating to interference harmonics caused by alternating current
(AC) on the power distribution lines. For utility usage reporting
and associated billing functions, the time-of-day can be an
important consideration. Moreover, the communications protocols
between the different layers of communications devices may require
time-based coordination between devices. The timing coordination
demands on the system can be significant as the data bandwidth of
the system increases (e.g., due, at least in part, to the
constraints caused by the use of power distribution lines). Aspects
of the present disclosure, although not necessarily limited to the
above characterizations and problems, are directed toward the
coordination of communications to endpoints. These communications
can use different time-bases and provide adjustments to the
communication protocol in order to account for such
differences.
[0022] Aspects of the present disclosure recognize that
transmitting symbols based upon a local oscillator can frustrate
reception of a downstream signal by an endpoint. This can also
cause inter-modulation harmonics relative to the transmit carrier
frequency. Other aspects of the present disclosure recognize that
using a symbol clock based solely upon the AC frequency can create
a host of time-based communication problems when coordinating
communications between pluralities of endpoint devices.
[0023] Example embodiments of the instant disclosure include
various methods, devices and systems. Consistent with the instant
disclosure, certain embodiments are directed towards a method
useful for coordinating communications between multiple endpoint
devices and multiple collector devices. The communications between
these endpoint devices and collector devices occurs over power
distribution lines (carrying power using alternating current (AC)).
In this method for coordinating communications, data is
communicated over the power distribution lines, from the collector
devices to the endpoint devices, utilizing a protocol that is
defined by a first timing and a second timing. The first timing
defines when data frames are transmitted, and the second timing
defines when the symbols within the data frames are transmitted.
Further, at each collector device, the method includes generating a
clock (e.g., from a local oscillator circuit), and, using the clock
as a time base, maintaining a collector network time. The first
timing is determined from the collector network time (at each
collector device). Additionally, at each collector device, the
frequency of AC carried on the power distribution lines is tracked.
The second timing is determined from tracked frequency. Moreover,
the method, of the instant embodiment, includes adjusting the
endpoint network time, at each endpoint device, in response to
time-indicating packet/data received from a collector device.
[0024] In certain embodiments, the method can further include
calculating the time from the end of a first frame (as determined
by the second timing) to the start of a second frame (as determined
by the first timing). An additional step of determining how many
synchronization symbols can be transmitted before the start of the
second frame is also included with the step of calculating the time
from the end of the first frame to the start of the second frame.
The number of synchronization symbols is determined based upon the
rate of symbol transmission for the first frame and the calculated
time. The network time can be adjusted in response to an externally
maintained standardized time, in certain embodiments.
[0025] In other example embodiments, the first timing defines when
data frames are transmitted, and thereafter, data symbols are
transmitted in response to a time-based parameter of the AC (e.g.,
a sensed frequency of the AC). The data symbols used in this method
useful for coordinating communications, in other example
embodiments, are encoded using quadrature phase shift keying
(QPSK). For embodiments using QPSK, the frequency of the AC can be
tracked by repeatedly (or periodically) executing code (e.g.,
operating an interrupt routine or polling routine) to sense a
signal value of the AC. The signal value can include, but is not
limited to, a (zero/nonzero) voltage crossing event, a
rising/falling edge, or (min/max) peak detection. For simplicity,
the repeated code is referred to hereafter as an interrupt routine.
This interrupt routine is operated at a rate that is sufficiently
fast to provide synchronicity for the encoded QPSK symbols to be
decoded at an endpoint that uses its own interrupt routine to sense
a signal value of the AC. The endpoint can then use the sensed
signal value for the purpose of determining the AC frequency.
[0026] Embodiments of the present disclosure are also directed
towards a method that includes maintaining a transmission period,
which has a start time and an end time synchronized to a network
time. Further, this method, in response to the start time, begins
transmission of a frame, which includes a plurality of symbols.
This transmission occurs over power distribution lines that carry
power using alternating current (AC). This method also includes
synchronizing a transmission time for each symbol of the plurality
of symbols with a corresponding signal transition of the AC. In
response to reaching an end of the frame, a synchronization symbol
period is determined for an adjusted synchronization symbol, as a
function of the transmission times, for the plurality of symbols
and time from the end of the frame to the end time. The adjusted
synchronization symbol is then transmitted over the power
distribution lines.
[0027] In certain specific embodiments of this method, each symbol
of the plurality of symbols has a common symbol period. Further,
the symbol period of the adjusted synchronization symbol is
different (less or greater) than the common symbol period. In those
instances, this method includes determining the synchronization
symbol period by determining a number of symbols of the common
symbol period that can be transmitted in the time from the end of
the frame to the end time. Accordingly, the adjusted
synchronization symbol can be used in combination with the
determined number of symbols of the common symbol period.
[0028] Embodiments of the instant disclosure are also directed
towards a device that includes a network time clock circuit, a
system time clock circuit, and a processing circuit. The network
clock circuit, of this device, is responsive to a network
time-of-day, and the system time clock circuit is responsive to a
frequency of an alternating current that is carried on power
distribution lines. The processing circuit is designed to determine
a transmission period having start and end times determined by
using the network time clock. Further, the processing circuit is
configured to begin transmission of a frame including a plurality
of symbols, in response to the start time and over power
distribution lines that carry power using alternating current (AC).
The processing circuit is designed to synchronize a transmission
time for each symbol of the plurality of symbols to the system time
clock. In response to reaching an end of the frame, the processing
circuit is designed to determine a symbol length for a
synchronization symbol as a function of time from the end of the
frame to the end time and transmission times for the plurality of
symbols. The processing circuit is configured to then transmit the
synchronization symbol on the power distribution lines.
[0029] Consistent with various embodiments of the present
disclosure, the power distribution lines can carry power that is
provided from one or more generating stations (power plants) to
residential and commercial customer sites alike. The generating
station uses AC to transmit the power long distances over the power
distribution lines. Long-distance transmission can be accomplished
using a relatively high-voltage. Substations located near the
customer sites provide a step-down from the high-voltage to a
lower-voltage (e.g., using transformers). Power distribution lines
carry this lower-voltage AC from the substations to the customer
sites. Depending upon the distribution network, the exact voltages
and AC frequencies can vary. For instance, voltages can generally
be in the range 100-240 V (expressed as root-mean-square voltage)
with two commonly used frequencies being 50 Hz and 60 Hz. In the
United States, for example, a distribution network can provide
customer sites with 120 V and/or 240 V, at 60 Hz.
[0030] FIG. 1 is a block diagram of an example network environment
100 in which endpoints 102 communicate data with collector units
104, consistent with embodiments of the present disclosure. The
network environment 100 includes a service network in which a
plurality of endpoints 102a-102f are coupled (e.g., communicatively
coupled) to collector units 104a, 104b. Consistent with embodiments
of the present disclosure, the endpoints 102 can provide data from
utility meters (101a, 101b). For instance, data can be provided
from power meters, gas meters and water meters, which are
respectively installed in gas and water distribution networks.
Moreover, while the present disclosure generally refers to the
endpoints 102 as providing data utility (e.g., power) metering over
a power distribution network, other data can also be
communicated.
[0031] The endpoints 102 can be implemented to monitor and report
various operating characteristics of the service network. For
example, in a power distribution network, meters can monitor
characteristics related to power usage in the network. Example
characteristics related to power usage in the network include
average or total power consumption, power surges, power drops and
load changes, among other characteristics. In gas and water
distribution networks, meters can measure similar characteristics
that are related to gas and water usage (e.g., total flow and
pressure).
[0032] The endpoints 102 report the operating characteristics of
the network over communications channels. Communications channels
are portions of spectrum over which data are transmitted. The
center frequency and bandwidth of each communications channel can
depend on the communications system in which they are implemented.
In some implementations, the communications channels for utility
meters (e.g., power, gas and/or water meters) can be transmitted
using power line communication networks that allocate available
bandwidth between endpoints according to an orthogonal frequency
division multiple access (OFDMA) spectrum allocation technique or
another channel allocation technique.
[0033] When the endpoints 102 are implemented in connection with
power meters in a power distribution network, the endpoints
transmit reporting data that specify updated meter information that
can include measures of total power consumption, power consumption
over a specified period of time, peak power consumption,
instantaneous voltage, peak voltage, minimum voltage and other
measures related to power consumption and power management (e.g.,
load information). Each of the endpoints can also transmit other
data, such as status data (e.g., operating in a normal operating
mode, emergency power mode, or another state such as a recovery
state following a power outage).
[0034] In some implementations, symbols (representing one or more
bits representing reporting and/or the status data) are transmitted
on the power distribution lines over a specified symbol period. A
symbol period is a period of time over which each symbol is
communicated. A number of symbols are contained within a frame
period, representing the time over which a complete frame is
communicated, wherein each frame provides synchronization for
symbols of the same frame.
[0035] In FIG. 1, endpoints 102a-102c and 102d-102f transmit
symbols over communications channels to collector units 104a, 104b,
respectively. The collector units 104 can include circuitry (e.g.,
including one or more data processors) that is configured and
arranged to communicate with the endpoints over power distribution
lines. The collector units 104 can also include circuitry for
interfacing with a command center 112. The interface to the command
center 112 can be implemented using a variety of different
communication networks including, but not limited to, a wide-area
network (WAN) using Ethernet.
[0036] According to certain embodiments of the present disclosure,
the collectors are installed in substations and used to control
bidirectional communication with both the command center 112 (e.g.,
located at a utility office) and endpoints (e.g., located at
metering locations for customer sites). This messaging to the
endpoints can be sent to an individual endpoint, or broadcast
simultaneously to a group of endpoints connected to the collectors
104. Consistent with certain embodiments, the collectors 104 are
built according to an industrial-grade computer specification in
order to withstand the harsh environment of a substation.
[0037] In certain embodiments of the present disclosure, the
collector(s) 104 can receive data from many different endpoints 102
while storing the data in a local database. A collector can also
take action based on the data received from the endpoints and
transmit data received from the endpoints to a command center 112.
For example, in a PLC network, the command center 112 can receive
data indicating that power usage is significantly higher in a
particular portion of a power network than in other portions of the
power network. Based on this data, the command center 112 can
allocate additional resources to that particular portion of the
network (i.e., load balance) or provide data specifying that there
is increased power usage in the particular portion of the power
network.
[0038] Consistent with certain embodiments, the command center 112
provides an interface that allows user devices 118 access to data
received from endpoints 102. For example, the user devices might be
owned by utility provider operator, maintenance personnel and/or
customers of the utility provider. For example, data identifying
the increased power usage described above can be provided to a user
device 118 accessible by the network operator, who can, in turn,
determine an appropriate action regarding the increased usage.
Additionally, data identifying a time-of-use measure and/or a peak
demand measure can also be provided to user devices 118. Similarly,
if there has been a power outage, the command center 112 can
provide data to user devices 118 that are accessible by customers
to provide information regarding the existence of the outage and
potentially provide information estimating the duration of the
outage.
[0039] The data networks 110a and 110b can each be a wide area
network (WAN), local area network (LAN), the Internet, or any other
communications network. The data networks 110 can be implemented as
a wired or wireless network. Wired networks can include any
media-constrained networks including, but not limited to, networks
implemented using metallic wire conductors, fiber optic materials,
or waveguides. Wireless networks include all free-space propagation
networks including, but not limited to, networks implemented using
radio wave and free-space optical networks. In certain embodiments,
the data networks 110 overlap with each other. In some embodiments,
they can be the same data network. For instance, each network 110
could provide data, at least in part, over the Internet.
[0040] Symbols from a particular endpoint may be transmitted over
anyone of thousands of communications channels in a PLC system. For
example, each endpoint can be assigned a particular channel using
OFDMA or another channel allocation technique. Channel assignments
for the endpoints 102a-102c, 102d-102f that communicate with
particular collectors 104a, 104b can be stored, for example, in an
communications database that is accessible to the command center
112 and/or the collectors 104a, 104b.
[0041] Consistent with embodiments of the present disclosure, each
collector 104 can be configured to be in communication with
thousands of endpoints 102 and there can be thousands of collectors
104 in connection with the command center 112. For example, a
single collector can be configured to communicate with over 100,000
endpoint devices and a command center can be configured to
communicate with over 1,000 collectors. Thus, there can be millions
of total endpoints and many thousands of these endpoints can
communicate to a common collector over a shared power distribution
line. Accordingly, embodiments of the present disclosure are
directed toward coordinating communications using carefully
designed time-based protocols and related considerations.
[0042] As a part of the instant disclosure, a method useful for
coordinating communication between the endpoint devices 102a-102f
and collector devices 104a-104b is discussed. The coordinated
communications between the endpoint devices 102a-102f and collector
devices 104a-104b occurs over power distribution lines that carry
power using alternating current (AC). This method includes
communicating data, over the power distribution lines, from the
collector devices 104a-104b to the endpoint devices 102a-102f
utilizing a protocol that is defined by a first timing and a second
timing. The first timing defines when data frames are transmitted,
and the second timing defines when the symbols within the data
frames are transmitted. In certain embodiments, the first timing
can be coordinated with an externally-provided time, such as
standardized time provided by a Coordinated Universal Time (UTC)
server 120. For instance, collector devices 104 can obtain
standardized time by directly accessing a UTC server 120 over the
Internet. In other instances, the command center 112 can access the
UTC server and then provide the time to the collectors 104. At each
collector device 104, the method further operates by generating a
collector clock (e.g., from a local oscillator circuit), and
maintaining a collector network time using the collector clock as a
time base. The collector determines the first timing from the
collector network time (at each collector device 104).
Additionally, at each collector device 104, the frequency of the AC
carried on the power distribution lines can be tracked or sensed.
Moreover, the method includes determining the second timing is
determined from the AC frequency. The method also includes
adjusting the endpoint network time, at each endpoint device
102a-102f, in response to time indicating packet/data received from
a collector device 104a-104b.
[0043] The method useful for coordinating communications can
include additional steps. For example, the method can further
include calculating the time from the end of a first frame to the
start of a second frame. The end of the first frame is determined
based on the second timing, and the start of the second frame is
determined based on the first timing. In these embodiments, an
additional step of determining how many synchronization symbols can
be transmitted before the start of the second frame is also
included with the step of calculating the time from the end of the
first frame to the start of the second frame. The number of
synchronization symbols is determined based upon the rate of symbol
transmission for the first frame and the calculated time. In
certain other embodiments, the network time is adjusted based upon
an externally maintained standardized time.
[0044] As used herein, the term metrology/metrological time denotes
a clock that keeps the time of day. For instance, the International
Bureau of Weights and Measures (BIPM) is responsible for
maintaining accurate worldwide time of day. It combines, analyzes,
and averages the official atomic time standards of member nations
around the world to create a single, official Coordinated Universal
Time (UTC). Such a clock is based upon a timescale that is designed
around the time of one rotation of the Earth. Such a design can
include compensation for mismatches between the (slowing) rotation
of the Earth and a particular timescale. While aspects of the
present disclosure are not necessarily reliant upon the specific
governing body that maintains such a metrological time, a
particular example thereof can be useful in discussing various
aspects of the present disclosure.
[0045] The first timing defines when data frames are transmitted
and data symbols are transmitted in response to sensing phases of
the AC thereafter in other example embodiments. In other example
embodiments, the data symbols used in this method can be useful for
coordinating communications that uses quadrature phase shift keying
(QPSK) encoding. The embodiments of this method that utilize QPSK
or other encoding protocols (e.g., amplitude shift keying,
differential phase shift keying or frequency shift keying) can
track the frequency of AC by periodically executing an interrupt
service routine (ISR) that monitors a sensed signal value of the
AC. This ISR can be operated at a rate that is sufficiently fast to
allow an endpoint to decoded QPSK symbols using another interrupt
routine to sense a signal value of the AC.
[0046] FIG. 2 depicts a block diagram for a device for coordinating
communications on power distribution lines, consistent with
embodiments of the present disclosure. A device 206 is configured
to transmit data on power distribution lines 216 using data
provided from processing circuit 212 to transceiver 218. In
particular embodiments of the present disclosure, the device 206 is
a collector device 104 that is configured to transmit to endpoint
devices 102. The processing circuit 212 generates symbol-encoded
data in which multiple symbols form a data frame. Each symbol
represents one or more data bits that are in turn represented by a
modulated carrier signal that is transmitted by transceiver 218
onto the power distribution lines. For instance, transceiver 218
can transmit symbols on power distribution lines 216 by modulating
phases of a carrier wave. The particular modulation is based upon
the symbol-encoded data, which was determined based upon the data
to be transmitted, and by the particular encoding scheme.
[0047] Aspects of the present disclosure recognize that the AC
transmitted on the power distribution lines can be used to help
maintain synchronicity between a collector and multiple endpoint
devices. Accordingly, the collector can be configured to use the AC
timings 208 as part of a second timing (the first operation being
discussed hereafter) operation 210. For instance, the symbol
period/frequency 222 for the encoded-symbols transmitted on the
power distribution lines can be set according to the AC timings. In
some instances, the endpoints can also be configured to monitor the
AC signal (locally) and use AC timings as a basis for their
respective decoding operations. The AC timings can be provided by
monitoring signal events, such as zero crossings, of the AC signal.
The zero crossings are but one example and others are possible,
such as detecting a particular non-zero signal value, signal edges,
and/or minimum/maximum signal values.
[0048] Other aspects of the present disclosure recognize that a
system time reference can be beneficial to coordinating
communications between endpoints and collectors. For instance,
operations such as meter readings rely upon the (metrology)
time-of-day (e.g., as relevant to billing and/or other reporting
aspects). Thus, aspects of the present disclosure are directed
toward the collector being configured to use another clock source
202 (e.g., a time-of-day clock using a local crystal oscillator) in
connection with a first timing operation 204. This first timing
operation 204 can be used to determine the start timing of frames
220, where the frames contain symbols using the second timing
operation 210. The clock source 202 can be maintained using a local
oscillator (or another timing source) while also being occasionally
updated based upon timing information received from a UTC server
(either directly or via command center 112).
[0049] Aspects of the present disclosure are also directed toward
compensating for differences between the second timing operation
210 and the first timing operation 204. For instance, the collector
206 can be configured and arranged to transmit using a data frame
that uses at least one synchronization symbol, having a
predetermined symbol period, to be transmitted before the start of
the data frame. For instance, a communication protocol may define
several synchronization symbols. These synchronization symbols will
be detected by a decoder and used to generate timing information
that is used to decode of subsequently transmitted data-carrying
symbols. The data-carrying symbols are then transmitted. Both the
synchronization symbol(s) and the data-carrying symbols use the
second synchronization operation 210; however, the start of the
data transmission is set using the first timing operation 204. At
the end of the data frame, the collector determines the time before
the data-carrying portion of the next data frame is to occur using
the first timing operation 204. From this determination, the
collector calculates a synchronization time during which
synchronization symbols are transmitted. The collector then
transmits a number of synchronization symbols that correspond to
the synchronization time.
[0050] Particular embodiments of the present disclosure are
directed toward communication protocols for which a symbol period
includes multiple signal events on the AC line. For instance, a
symbol can be transmitted over a symbol period corresponding to 4
zero crossings. In such an instance, the collector determines how
many synchronization symbols to transmit based upon the number of
zero crossings that are expected to occur during the calculated
synchronization time and the symbol period. More particular
embodiments determine when the number of expected zero crossings is
not evenly divisible by the symbol period. For instance, a symbol
period of 4 zero crossings would not be evenly divisible relative
to an expected number of zero crossings that is 17. For such a
situation, there could be 4 symbols (16 zero crossings) leaving one
zero crossing extra. Accordingly, embodiments of the present
disclosure adjust the symbol period for one symbol to accommodate
the one extra zero crossing. This adjustment could include either
lengthening or shortening the symbol period.
[0051] Certain embodiments of the present disclosure allow for the
adjustment of the symbol period to be independent of endpoint
configuration. Thus, the endpoint need not be configured to decode
a symbol that has the adjusted period. The subsequent
synchronization symbols, however, can be transmitted using the
correct/common symbol period and therefore can be decoded by
endpoints.
[0052] FIG. 3 depicts a timing diagram for frames transmitted over
power distribution lines, consistent with embodiments of the
present disclosure. The transmission period 300 includes data
portion 310 and synchronization portion 320. As depicted in FIG. 3,
the beginning of the data portion 310 is synchronized according to
a network time, which would correspond to a first synchronization.
The particular symbols 302 within the data portion 310 are
synchronized according to a system time. In particular embodiments,
the system timing is based upon the frequency of AC on the power
distribution lines (e.g., obtained by monitoring zero crossings).
The symbol period is set by, and varies according to, the frequency
of the AC (e.g., defined as a set number of zero crossings). Each
data symbol 302 can thus be transmitted using the AC as a timing
reference.
[0053] When the end of the data portion 310 is reached, the
synchronization length 330 can be determined based upon the current
time and the start time for the data portion of the next frame 308.
This start time is based upon network timing (e.g., local
oscillator and metrology time). A certain number of synchronization
symbols 306 are determined as being able to be transmitted during
the synchronization length 330. The collector can also determine
whether an adjusted symbol period for one symbol 304 would provide
better synchronization.
[0054] FIG. 4 depicts a timing diagram for coordinated
transmissions, consistent with embodiments of the present
disclosure. In a particular embodiment of the present disclosure,
the collector calculates how much time there is until the beginning
of the minute of the network clock. Thus, the
collector-to-endpoints are synchronized to provide one frame per
minute. Timeframes other than a minute can also be used. Then, the
collector predicts how many line crossings it will take to reach
the beginning of the minute. Alternative embodiments may not
expressly calculate a number of line crossings. For instance, the
timing could be based upon a predicted symbol period as adjusted
for the frequency of the AC. This prediction can be accomplished,
for example, using an average frequency of line crossings for the
last minute (or over another period of time). It then correlates
the number of predicted line crossings with the number of line
crossings per symbol (the symbol period). If the result is an
integer, the collector is configured to output the appropriate
number of symbols in order to reach the beginning of the next
minute. If the calculation results in a number of symbols that
would go past the beginning of the minute, the first symbol of the
synchronization period is shortened by the appropriate number of
zero crossings to result in synchronization period transmission
that ends as close to the beginning of the minute as possible.
Alternatively, if the calculation results in a number of symbols
that ends before the beginning of the minute, an additional symbol
is added, which contains the appropriate number of zero crossings
to result in synchronization period transmission that ends as close
to the beginning of the minute as possible. In either event, the
altered symbol can be transmitted before the unaltered symbols (or
any time before a minimum number of synchronization symbols used as
part of the communication protocol).
[0055] According to certain embodiments, the synchronization
symbols can be followed by a start bit. An endpoint that receives a
series of synchronization symbols will wait for receipt of a start
bit, which indicates the beginning of the data-carrying portion of
the frame. In the diagram of FIG. 4 this start bit would be
provided at the beginning of the minute--network time.
[0056] Consistent with embodiments of the present disclosure, the
collector includes a processor circuit that is configured and
arranged using software-programmed instructions. These
software-programmed instructions can include, but are not limited
to, an interrupt service routine (ISR) or a polling procedure that
is called/ran at a rate sufficient to synchronize actions with the
frequency of the AC. For instance, the call rate of the ISR can be
10 kHz. This rate is not limiting and various other rates can be
implemented depending upon factors such as the fidelity of the AC
signal and the processing speed of the processor circuit, e.g.,
including, but not limited to rates of 1 kHz and higher. For
instance, the rate can be set according to the ability of the ISR
to reliably check for AC zero crossing events. In one embodiment, a
line crossing flag can be set independent of the ISR whenever a
power line zero crossing has been detected. The ISR can then check
for this flag bit to determine the appropriate action. For
instance, the ISR can count the number of flag bits detected since
the previous symbol was modulated. When the count reaches a set
number (the symbol period of the transmitter), the next symbol in
the frame can be modulated.
[0057] FIG. 5 depicts a flow diagram for an ISR, consistent with
embodiments of the present disclosure. The algorithm corresponding
to this flow diagram can be useful to describe certain aspects of
the present disclosure. This algorithm, however, is a specific
example and does not necessarily limit the scope of other
embodiments discussed herein. For instance, a (periodic or
event-triggered) polling procedure can be used.
[0058] At block 502 the ISR is entered. In certain embodiments of
the present disclosure, the ISR can be entered periodically, e.g.,
in response to a timer event. At blocks 506, the processor circuit
can determine if a (AC) line-crossing event has occurred since the
last ISR was entered. This can be accomplished, for example, by
reading, per block 504, a flag or register that is set in response
to a line-crossing event. A line-crossing event can represent a
zero-crossing event, or other non-zero crossing points.
Alternatively, other phase-related detections can be used, such as
min-max detection to detect signal peaks of the AC.
[0059] If no line-crossing (or equivalent) event has occurred, then
a current value for the transmission signal (sample) can be sent to
a digital-to-analog converter (DAC) for transmission on a power
distribution line. For instance, the communication protocol can
operate by modulating one or more carrier waves. The current state
of the carrier wave (e.g., the current phase for a
phase-shift-keyed protocol) determines the sample that is sent to
the DAC. Block 508 therefore represents a situation where there is
no need to modulate the carrier wave (e.g., the next symbol period
has not been reached). The ISR can then be exited at block 510.
[0060] If a line-crossing event has occurred, then the
line-frequency interrupt counter can be incremented and the
line-crossing flag can be cleared as shown by block 512. The
line-frequency interrupt counter keeps track of the number of
line-crossings that have occurred during the current symbol period.
Accordingly, block 514 represents a check on whether or not the
frequency interrupt counter indicates that the next symbol period
has been reached (e.g., by comparing the frequency interrupt
counter to a threshold value representative of the symbol period).
As an example, the symbol period could be set to 10 line crossing
events. The frequency interrupt counter would then need to have
been incremented 10 times before meeting the symbol threshold. If
the current symbol period is not indicated as having been
completed, then the ISR moves to block 508. If, however, the
current symbol period is indicated as having been completed, then
the ISR advances to block 516.
[0061] At block 516, the ISR checks whether the transmission is in
a synchronization portion/period or data portion/period of a
current frame. In certain embodiments, this check can be
accomplished by reading a flag or register that is set when a
synchronization period begins. If the current period is not
determined to be a synchronization period, the ISR advances to
block 518. If the current period is determined to be a
synchronization period, the ISR advances to block 524.
[0062] At block 518 the ISR checks whether or not the end of a
data-portion of a current frame has been reached (e.g., by checking
a frame count against a threshold value). If not, then the ISR
would advance to block 520 in order to provide the next data
symbol. At block 520, the ISR determines the modulation for the
next data symbol. For instance, a phase-shift-keyed modulation
scheme would involve determining the new phase for a carrier wave.
The ISR would also keep track of the current location within a
frame (e.g., by incrementing the frame count). Once the modulation
(phase) is determined, the resulting sample is then provided to the
DAC at block 508.
[0063] At block 522, the ISR determines the synchronization length.
This determination can be a function of the current network time,
the symbol period, the average AC frequency over the past frame(s),
and the network time corresponding to the desired start for data
portion of the next frame. FIG. 6 and the forthcoming discussion
thereof provide more details of example synchronization calculation
algorithms for determining the average AC frequency.
[0064] At block 524, the ISR determines whether the current
synchronization period has reached an end (e.g., by checking a
synch period count value or by checking a start data frame flag).
If the period has not ended, then the modulation for the next
synchronization symbol is determined (e.g., the proper phase) at
block 526 and, if necessary, a symbol count value is incremented to
represent that the next synchronization symbol period has been
entered. The resulting sample is then provided to the DAC at block
508.
[0065] At block 528, the ISR has determined that the current
synchronization period is over and that the next data period has
begun. Accordingly, the synchronization period flag can be
reset/set to false. The modulation for the start of the data period
can also be determined, e.g., by determining the value for a start
bit that will be recognized by downstream endpoints. The sample
corresponding to this modulation can then be provided to the DAC at
block 508.
[0066] FIG. 6 depicts a flow diagram for an AC line-frequency ISR
that can be used to determine the average line frequency of that
AC, consistent with embodiments of the present disclosure.
Consistent with embodiments of the present disclosure, the
collector is configured to account for variation in the
line-frequency of the AC over time and/or a lack of synchronization
between the AC frequency and the network time. For instance, the
collector can predict the number of line crossing events that will
occur between the end of a current data frame and the start of the
next data frame (determined based upon network time). This
prediction uses the past AC frequency to predict the future AC
frequency. For instance, the AC line-frequency ISR is entered at
block 602 in response to detection of a line-crossing (or
equivalent) event. At block 604, the AC line-frequency ISR
determines the time since the last line-crossing event occurred. In
certain embodiments, this determination can be made by accessing a
high-resolution timer. For instance, the high-resolution timer can
be free running relative to the AC timings and the current value
can be compared to a value corresponding to a previous
line-crossing event to determine the elapsed time. The
high-resolution timer can also be reset upon a valid line-crossing
event.
[0067] Block 606 represents a determination of whether or not the
line-crossing event is valid. If, for example, the current
line-crossing event is not within an acceptable range, this may
indicate that the line-crossing event was caused by noise or other
unwanted interference. In such an instance, the AC line-frequency
ISR can exit at block 610 and not use the current (invalid)
line-crossing event to calculate the AC line-frequency. If,
however, the current line-crossing event is within an acceptable
range of time, the AC line-frequency ISR proceeds to block 608. At
block 608, the AC line-frequency ISR updates the AC line-frequency
using the timing of the current line-crossing event. This
information can be used in a number of manners including, but not
necessarily limited to, a running average of the AC line-frequency.
More sophisticated averaging algorithms can also be used.
[0068] The signals and associated logic and functionality described
in connection with the figures can be implemented in a number of
different manners. Unless otherwise indicated, various
processor-based systems and/or logic circuitry (sometimes referred
to as logic modules or software-based computer modules) may be used
with programs in accordance with the teachings herein, or it may
prove convenient to construct a more specialized apparatus to
perform the required method. For example, according to the present
disclosure, one or more of the methods can be implemented in
hard-wired circuitry by programming a general-purpose processor,
other fully or semi-programmable logic circuitry, and/or by a
combination of such hardware and a general-purpose processor
configured with software.
[0069] It is recognized that aspects of the disclosure can be
practiced with computer/processor-based system configurations other
than those expressly described herein. The required structure for a
variety of these systems and circuits would be apparent from the
intended application and the above description.
[0070] The various terms and techniques are used by those
knowledgeable in the art to describe communications, protocols,
applications, implementations, mechanisms, etc. One such technique
is the description of an implementation of a technique expressed in
terms of an algorithm or mathematical expression. That is, while
the technique may be, for example, implemented as executing code on
a computer, the expression of that technique may be more aptly and
succinctly conveyed and communicated as a formula, algorithm, or
mathematical expression.
[0071] Thus, it is recognized that a block denoting "C=A+B" as an
additive function whose implementation in hardware and/or software
would take two inputs (A and B) and produce a summation output (C),
such as in combinatorial logic circuitry. Thus, the use of formula,
algorithm, or mathematical expression as descriptions is to be
understood as having a physical embodiment in at least hardware
(such as a processor in which the techniques of the present
disclosure may be practiced as well as implemented as an
embodiment).
[0072] In certain embodiments, machine-executable instructions can
be stored for execution in a manner consistent with one or more of
the methods of the present disclosure. The instructions can be used
to cause a general-purpose or special-purpose processor that is
programmed with the instructions to perform the steps of the
methods. Alternatively, the steps might be performed by specific
hardware components that contain hardwired logic for performing the
steps, or by any combination of programmed computer components and
custom hardware components.
[0073] In some embodiments, aspects of the present disclosure may
be provided as a computer program product, which may include a
machine or computer-readable medium having stored thereon
instructions which may be used to program a computer (or other
electronic devices) to perform a process according to the present
disclosure. Accordingly, the computer-readable medium includes any
type of media/machine-readable medium suitable for storing
electronic instructions.
[0074] The various embodiments described above are provided by way
of illustration only and should not be construed to limit the
disclosure. Based on the above discussion and illustrations, those
skilled in the art will readily recognize that various
modifications and changes may be made to the present disclosure
without strictly following the exemplary embodiments and
applications illustrated and described herein. For instance, such
changes may include variations on mechanisms for synchronization
with (and/or tracking of) the AC line frequency. Such modifications
and changes do not depart from the true spirit and scope of the
present disclosure, which is set forth in the following claims.
* * * * *